Question

我有以下代码......

void draw_polygon(struct vector2d* center, int num_points,
              struct vector2d* points, int mode)
{
    int i;

    if(mode == GL_TRIANGLE_FAN)
      glVertex2f(center->x, center->y);

    for(i = 0; i < num_points; i++)
      glVertex2f(points[i].x, points[i].y);

    glVertex2f(points[0].x, points[0].y);
}

我试图转换它，因此它是OpenGLES 1.1 compat。从其他帖子我觉得我觉得我需要类似的东西......

void draw_polygon(struct vector2d* center, int num_points,
              struct vector2d* points, int mode)
{
  int i;
  int offset=0;
  GL_FLOAT *arr;
  if(mode == GL_TRIANGLE_FAN)i{
    *arr = (GL_FLOAT *)malloc(sizeof(GL_FLOAT) * ((num_points+1)*2));
    arr[0]=center->x;
    arr[1]=center->y;
    offset = 2;
  }
  else{
    *arr = (int *)malloc(sizeof(GL_FLOAT) * (num_points*2)) ;
  }

  for(i = 0; i < num_points; i++){
    int g = i+offset;
    arr[g]=points[i].x;
    arr[g+1]=points[i].y;
    i++;
  }
}

但当然不能编译。有人可以帮我理解在GLES中处理这个问题的正确方法吗？

Answer 1

关于不编译的冷杉：

struct vector2d {
    GLfloat x, y;
};
void draw_polygon(struct vector2d* center, int num_points,
                  struct vector2d* points, int mode)
{ //1st GL_FLOAT is not a type, use GLfloat
    int i;
    int offset=0;
    GLfloat *arr;
    if(mode == GL_TRIANGLE_FAN) { //what was that "i" doing here
        arr = (GLfloat *)malloc(sizeof(GLfloat) * ((num_points+1)*2)); //no "*" before arr
        arr[0]=center->x;
        arr[1]=center->y;
        offset = 2;
    }
    else{
        arr = (GLfloat *)malloc(sizeof(GLfloat) * (num_points*2)) ;  //no "*" before arr; Why do you typcast it to "(int *)"?
    }

    for(i = 0; i < num_points; i++){
        int g = (i*2)+offset;//i*2
        arr[g]=points[i].x;
        arr[g+1]=points[i].y;
        i++;
    }
}

至于做整个代码。 GLES不支持开始/结束通话，但您必须调用绘图调用。此时使用上面的代码创建了一个顶点数据数组，现在需要将其推送到GPU（或设置数据的指针）并调用glDrawArrays。

所以你需要添加：

    glEnableClientState(GL_VERTEX_ARRAY); //this is usually set only once unless you want to disable it at some point for some very unlikelly reason
    glVertexPointer(2, GL_FLOAT, 0, arr); //set the pointer (alternative is to use the VBO and copy the data directly to the GPU)
    glDrawArrays(mode, 0, num_points+offset/2);

    free(arr); //you need to free the allocated memory

在同一个功能中。

为了使你的方法看起来不那么复杂，你可以试试这个：

void draw_polygon2(struct vector2d* center, int num_points, struct vector2d* points, int mode) {
    if(mode == GL_TRIANGLE_FAN) {
        vector2d *newBuffer = (vector2d *)malloc(sizeof(vector2d)*(num_points+1));//create a new buffer just to append center to beginning
        newBuffer[0] = *center; //copy center
        memcpy(newBuffer+1, points, sizeof(vector2d)*num_points); //copy all other points after center
        glEnableClientState(GL_VERTEX_ARRAY);
        glVertexPointer(2, GL_FLOAT, sizeof(vector2d), newBuffer);
        glDrawArrays(mode, 0, num_points+1);
        free(newBuffer);
    }
    else {
        glEnableClientState(GL_VERTEX_ARRAY);
        glVertexPointer(2, GL_FLOAT, sizeof(vector2d), points);
        glDrawArrays(mode, 0, num_points);
    }
}

请注意，由于此函数直接使用vector2d结构，因此认为x和y是vector2d结构中的前2个参数。即使你添加'z'作为第三个参数，代码应该可以工作。

如何：从OpenGL转换为GLES

1 个答案: